1. Field of the Invention
The present invention relates to a water-cooled V-type engine with two cylinders, and particularly to the piping and cooling devices of a cooling system included in the engine.
2. Description of the Related Art
In a water-cooling system of a water-cooled V-type engine with two cylinders, a thermostat valve is disposed generally at the outlet of a water jacket formed in the cylinder head of a cylinder so as to protrude from one side of the cylinder. The thermostat valve measures the temperature of cooling water at the outlet of the water jacket during a warm-up or during a normal operation. The thermostat valve opens when the temperature of the cooling water is higher than a predetermined temperature to return the cooling water discharged through the outlet of the water jacket to a radiator and to supply the cooled cooling water flowed through the radiator to the water jacket of the cylinder.
In the water-cooling system including the thermostat valve disposed at the outlet of the water jacket, especially in warm-up operation, the thermostat valve opens upon the increase of the temperature of the cooling water to the predetermined temperature and the cooled cooling water flowed through the radiator flows suddenly into the water jacket. Consequently, the cylinder is cooled suddenly and the temperature of the cooling water is apt to hunt. Particularly in a state where the atmospheric temperature is low or a cooling fan is continuously rotating, the temperature of the cooling water hunts in a very wide temperature range.
On the other hand, as shown in FIG. 5, a water-cooling system with a thermostat valve disposed at the inlet of a water jacket, so called xe2x80x9can inlet thermostat type water-cooling systemxe2x80x9d, is disclosed in Japanese Utility Model Publication No. Sho 63-12626. In this system, the thermostat valve 110 is placed in a water supply pipe 105 having one end connected to a water outlet 103 formed at a lower end part of a radiator 102 and the other end connected to the water inlet 107 of a water jacket 106.
When the thermostat valve 110 is thus placed in the cooling water supply pipe 105, the thermostat valve 110 operates according to the temperature of the cooling water discharged from the water jacket 106 and flowed through a bypass passage 108, to mix the cooling water of a low temperature supplied from the radiator 102 and the cooling water of a high temperature discharged from the water jacket 106 and flowed through the bypass passage 108. Accordingly, the mixed cooling water of a substantially fixed temperature flows into the water jacket 106. Thus the sudden variation of the temperature of the cylinder can be avoided and the hunting of the temperature of the cooling water can be prevented.
However, in the inlet thermostat type water-cooling system shown in FIG. 5, when the cooling water is supplied to the water-cooling system through a filler opening 112 formed in the radiator 102, the cooling water is unable to flow past the thermostat valve 110 into the water jacket 106. Therefore, an auxiliary filler opening 120 must be formed in an upper end part of the water jacket 106 and the cooling water must be supplied through the auxiliary filler opening 120 into the water jacket 106, which requires additional work.
Moreover, when draining the cooling water from the water-cooling system, all the cooling water cannot be drained through a drain port 113 formed in the radiator 102. Accordingly, the cooling water must be drained also through a secondary drain port 121 formed in a lower end part of the water jacket 106.
Accordingly, it is an object of the present invention to provide a water-cooled V-type engine with two cylinders including a cooling system capable of stabilizing the temperature of the cooling water to prevent the hunting of cooling water, of enabling forming the engine in compact construction and of facilitating work for supplying cooling water to the cooling system and for draining the cooling water from the cooling system.
According to a first aspect of the present invention, a water-cooled V-type engine includes: a crankcase in which a crankshaft is rotatably disposed; two cylinders disposed on the crankcase so as to form V-shape; a starter disposed below one of the two cylinders; and a cooling system for cooling the engine with a cooling water. The cooling system includes: a radiator for cooling the cooling water; water jackets disposed on the two cylinders; and a thermostat disposed in a supply line having one end connected to a water outlet formed in a lower end part of the radiator and the other end connected to inlets of the water jackets. The thermostat is disposed below the other of the two cylinders.
Since the thermostat is disposed at the side of the inlet of the water jacket, the temperature of the cooling water can be stabilized and the hunting of the temperature of the cooling water can be prevented, moreover, since the starter and the thermostat are disposed below the tilted cylinders, respectively, the engine can be formed in compact construction and the piping of the cooling system can be simplified.
Preferably, the water-cooled V-type engine with two cylinders according to the first aspect of the present invention further includes a water pump disposed in the supply line for forcing the cooling water. The radiator is disposed on one side of the engine with respect to an axial direction of the crankshaft. The water pump is disposed on the other side of the engine with respect to the axial direction of the crankshaft. The thermostat is disposed in the supply line between the radiator and the water pump.
Thus the piping of the cooling system can be simplified.
Preferably, in the water-cooled V-type engine with two cylinders according to the first aspect of the present invention, the thermostat is disposed so that a center of the thermostat is located in a width range corresponding to an axial dimension of the cylinder.
Preferably, the water-cooled V-type engine with two cylinders according to the first aspect of the present invention further includes: a bypass line adapted to supply the cooling water to the water jackets and drain the cooling water from the water jackets, the bypass line connecting lower end parts of the water jackets with a lowermost part of the supply line between the water outlet of the radiator and the thermostat, and a check valve for preventing a reverse flow of the cooling water from the water jackets to the supply line.
Thus both the radiator and the water jackets can be simultaneously filled up with the cooling water simply by pouring the cooling water through a filler opening of the radiator into the radiator and the cooling water can be efficiently supplied to the cooling system.
Preferably, in the water-cooled V-type engine with two cylinders according to the first aspect of the present invention, a drain port capable of being opened and closed is formed in a lowermost part of the bypass line.
Thus, both the radiator and the water jackets can be simultaneously drained only through the single drain port to achieve draining work efficiently.
According to a second aspect of the present invention, a water-cooled V-type engine includes: a crankcase in which a crankshaft is rotatably disposed; two cylinders disposed on the crankcase so as to form V-shape; a cooling system for cooling the engine with a cooling water. The cooling system includes a radiator for cooling the cooling water, water jackets disposed on the two cylinders, and a thermostat disposed in a supply line having one end connected to a water outlet formed in a lower end part of the radiator and the other end connected to inlets of the water jackets. The engine further includes: a bypass line adapted to supply the cooling water to the water jackets and drain the cooling water from the water jackets, the bypass line connecting lower end parts of the water jackets with a lowermost part of the supply line between the water outlet of the radiator and the thermostat; and a check valve for preventing a reverse flow of the cooling water from the water jackets to the supply line.
Thus both the radiator and the water jackets can be simultaneously filled up with the cooling water simply by pouring the cooling water through a filler opening of the radiator into the radiator and the cooling water can be efficiently supplied to the cooling system.
Preferably, in the water-cooled V-type engine with two cylinders according to the second aspect of the present invention, a drain port capable of being opened and closed is formed in a lowermost part of the bypass line.
Thus, both the radiator and the water jackets can be simultaneously drained only through the single drain port to achieve draining work efficiently.